> In practice, just like everything in engineering, you don't run your grid at 50 Hz nor your railroad at 50/3 Hz. You run the grid at some frequency that varies slightly around 50Hz. There's always engineering tolerances.

> So even if you don't like rational numbers, it doesn't really matter whether you run the railroads at 50/3 +-0.01 Hz, or at 16.66 +-0.01 Hz.

In practice the nominal frequency was changed to 16.7 Hz anyway due to some weird edge case created when running motor-generators [1] for prolonged periods of time at exactly the nominal 3:1 frequency conversion ratio. (See https://de.wikipedia.org/wiki/Bahnstrom#16_2%E2%81%843_Hz_ge... and use an online translator at your own peril if necessary.)

[1] These days, newly built (or probably occasionally re-built) substations prefer to use solid-state frequency converters, which are immune to this particular problem, but there still are enough of the older motor-generator sets around, too. Wikipedia also claims that motor-generator sets are more tolerant against earth faults, which might or might not preclude against getting rid of all of them even long-term.